Kinetics model for thermal selective etching of Si1−xGex in F2/Ar

The selective etching of Si1−xGex over Si enables the fabrication of the gate-all-around field-effect transistors. While ample experimental data have confirmed such selectivity in various halogen-based chemistries, a mechanistic understanding of its origin is lacking. In this work, a kinetics model was developed to explain the volcano-shaped etch rate and selectivity in etching Si1−xGex in F2/Ar at near room temperature, as the germanium composition (Ge%) changes from 0% to 100%. The key reactions dictating this unique etch characteristic are GeF4(g) etching of Si and the formation of nonvolatile (GeF2)n. The competition and balance between these reactions successfully explained the rapid increase in etch rate/selectivity at Ge% below 20% and the decrease at higher Ge% over a wide pressure range (0.5–10 mTorr).